As known in the art, electrical storage devices such as lithium ion capacitors which exhibit characteristics including high capacity, high energy density and high output have been recently used in electric vehicles and hybrid vehicles. In a lithium ion capacitor, a negative electrode capable of storing and releasing lithium ions is brought into contact with a lithium ion supply source such as lithium metal to store or carry (to be pre-doped with) lithium ions physically or electrochemically. The pre-doping lowers the negative electrode potential, resulting in a high withstand voltage and a high energy density.
In order to obtain further improvements in the performances of lithium ion capacitors, a lithium ion capacitor is disclosed in which a decrease in resistance is sought by forming a positive electrode using a fluorine-modified acrylic binder (see Patent Literature 1).
Although such lithium ion capacitors exhibit good output characteristics, demands have been placed on a further decrease in resistance as well as on higher capacity and higher reliability in order to achieve greater proliferation of these capacitors.